1. Field of the Invention
The present invention relates to a shaft coupling structure and a method for manufacturing a divided spline to be used in the shaft coupling structure. More specifically, it relates to a shaft coupling structure used, for instance, for coupling a brake center to a drive shaft in a mechanical press, and a method for manufacturing a divided spline to be used in the shaft coupling structure.
2. Description of Related Art
There has been used a mechanical engaging structure adopting an involute spline, as a coupling structure for transmitting a torque between a clutch center and a drive shaft and between a brake center and a drive shaft.
In this type of structure, involute splines have some backlash (.e., slack or gap in the operational direction) therebetween from the first. Further, in such a structure, the spline portions are worn by usage over years, resulting in a larger backlash. To overcome the above, it is conceivable to zero out the backlash, but this is impractical, such as due to difficulty in assembling. As a result of the above circumstances, sufficient power from a drive shaft is hardly transmitted to its associated member, resulting in the replacement of a drive shaft, for example. This has problematically required a lot of repair cost.
Meanwhile, there has been also used a coupling structure based on a friction coupling such as a span-ring. This coupling structure based on the friction coupling has been widely used, since the structure has such advantages that it is easy to conduct positioning and phasing, the backlash after jointing is zero, and the machining cost is low.
Incidentally, in case of a friction coupling, the transmission torque depends on a clamping torque and on friction coefficients of the friction transmitting portions. As such, there is caused slippage in the friction coupling such as due to: wear-out of engaging surfaces by repeated loads of transmission torques and usage over years; reduction of a clamping force such as by vibration; and errors of a clamping operation. This results in a problem of an insufficient torque, thereby failing to provide sufficient reliability of the transmission torque.
It is therefore an object of the present invention to provide a shaft coupling structure which restricts slippage while conducting power transmission in a friction manner, to thereby provide an optimum and sufficient transmission torque.
It is another object of the present invention to provide a method for manufacturing a divided spline usable in the above shaft coupling structure, with higher precision.
Accordingly, the present invention provides a shaft coupling structure for transmitting a rotary power between a shaft-side member and a boss-side member, the shaft coupling structure comprising: friction-type main power transmitting means provided between the shaft-side member and the boss-side member; and auxiliary power transmitting means provided adjacent to the main power transmitting means so as to mechanically engaging the shaft-side member with the boss-side member.
According to such a constitution of the present invention, there can be conducted backlash-free transmission by the friction coupling by adopting the friction coupling as the main power transmitting means and the mechanical engaging means as the auxiliary power transmitting means, and there can be conducted torque transmission by the mechanical engaging means even upon occurrence of slippage in the friction coupling, thereby obtaining sufficient reliability of transmission torque.
In the present invention, the main power transmitting means may be any type structure of friction coupling insofar as capable of ensuring a suitable transmission torque, such as utilizing a span-ring, shrink fit and cooling fit.
As the auxiliary power transmitting means, there can be adopted various mechanical engaging means such as a key connection, pin connection, and spline connection.
In the shaft coupling structure of the present invention, the auxiliary power transmitting means preferably has a predetermined gap in the rotational direction.
In such a constitution of the present invention, the auxiliary power transmitting means based on mechanical engagement has a predetermined gap in the rotational direction, so that the torque transmission under a normal condition is conducted, not by the auxiliary power transmitting means, but exclusively by the friction-type main power transmitting means. Thus, those parts constituting the auxiliary power transmitting means can be kept from the affection of repeated loads of transmission torques, thereby allowing to prevent wear and damage of the constituent parts of the auxiliary power transmitting means and to restrict the depletion of the parts.
In the shaft coupling structure of the present invention, the auxiliary power transmitting means preferably comprises a divided spline.
This enables assured torque transmission of a large amount, and allows a simplified mechanism.
In the shaft coupling structure of the present invention applied to a brake device of a press machine, the drive shaft of the brake device is preferably the shaft-side member and the brake center of the brake device is preferably the boss-side member.
In this way, the above described shaft coupling structure of the present invention is applied to between the drive shaft and brake center constituting the brake device of the mechanical press where it is required to transmit a large torque with high precision, so that the effect of the shaft coupling structure of the present invention can be maximally utilized.
Further, even upon occurrence of slippage in the friction coupling as the main power transmitting means such as due to usage over years, there can be assuredly conducted the torque transmission by the auxiliary power transmitting means, so as to prevent trouble of the brake, thereby achieving a mechanical press having higher safety.
The present invention further provides a method for manufacturing a divided spline usable as the auxiliary power transmitting means constituting the shaft coupling, comprising the steps of: finishing both end surfaces of a toroidal member as a blank of the divided spline; cutting the toroidal member as the blank in the radial direction thereof to thereby divide the toroidal member into a predetermined number of divided parts, and finishing the cut surfaces of the divided parts; and assembling the divided parts by a jig while mating the cut surfaces with each other, and splining at least the inner peripheries of the respective divided parts.
According to such a constitution of the present invention, the divided spline is constituted of a predetermined number of divided parts, so that the divided spline can be later mounted onto the shaft-side member, to thereby simplify the mounting.
Although the divided spline is constituted of such a predetermined number of divided parts, the divided spline can be manufactured with higher precision because the divided parts are splined in a state assembled by a jig(s).
Preferably, the manufacturing method for manufacturing a divided spline of the present invention further comprises the steps of: before dividing the toroidal member, marking thereon a circle having a diameter taking account of cutting margins and finishing margins, and machining, on the marked circle, hole positions for coupling to the jig.
According to such a constitution of the present invention, assembling of the divided parts and jig can be facilitated.